An infrared sensor array system is developed to detect and track a person. This system is applicable for finding shopliftings in the stores and for monitoring the mobility of a person for the healthcare purpose. Since the sensor detects human body radiation, no signal transmission equipment is necessary for the target person. Pyroelectric sensors were applied to detect the human body radiation. Based on the experiment which was carried out by single pyroelectric sensor, a trial system was fabricated and tracking performance was measured using 22 pyroelectric sensors. In order to achieve better accuracy, the detecting area was optimized and experiments were carried out for various walking routes. Since the pyroelectric sensor detects the change of infrared intensity, the sensor can not detect the person if he/she does not move. To solve this problem, a new detecting algorithm was developed.